1. Field of the Invention
The present invention relates to hearing aids for use by hearing-impaired persons, and in particular to a hearing aid having an adjustable frequency response.
2. Description of the Prior Art
Hearing aids are known which include a plurality of frequency selecting channels connected to the output of a microphone which receives incoming audio signals. Such hearing aids are described, for example, in German OS 30 27 953, Published European Application 00 76 687 and Published PCT Application 83/02212. In German OS 30 27 953, for example, frequency responses are set during a testing phase, the hearing aid then operating according to this frequency response during subsequent use. The selected frequency response may be, for example, that of a conversation partner.
European Published Application 00 76 687 discloses a similar hearing aid which also includes two sets of bandpass filters. In the testing mode, the desired frequency response is filtered out by the first of the two sets of bandpass filters. The second set of bandpass filters, dependent upon the operation of the first set, is then set such that frequencies in the range of voices are preferentially influenced. The hearing aid automatically tunes during subsequent use to the previously selected frequency spectrum. The wearer of the hearing aid, for example, may concentrate entirely on the conversation partner, whose frequency spectrum is preferentially filtered out of the ambient noises by the hearing aid particularly in an extremely loud environment.
In the hearing aid disclosed in PCT Published Application 83/02212, each frequency channel operates according to a respective stored dynamic characteristic. The signal is influenced by means of dynamic compression.
It is known that hearing-impaired persons have a reduced time resolution capability. Because of slower signal decay times associated with hearing-impaired persons, adequate speech resolution cannot be achieved by such persons without auxiliary means.